suppressing highs at the speaker

All speakers have the limitation of the high frequency response. I have two questions: 1) If a speaker is rated for say 30 to 15k hz response, how much of that can actually be heard (on the high end of course)? 2) Because the highest frequency response is most likely a function of the weight of the moving voice coil and cone, inertia, wouldn't increasing that inertia take out some of the highs? I suppose that another piece of the response is reactance of the voice coil. Any thoughts?

All speakers have the limitation of the high frequency response. I have two questions: 1) If a speaker is rated for say 30 to 15k hz response, how much of that can actually be heard (on the high end of course)? 2) Because the highest frequency response is most likely a function of the weight of the moving voice coil and cone, inertia, wouldn't increasing that inertia take out some of the highs? I suppose that another piece of the response is reactance of the voice coil. Any thoughts?

1) It depends on the speaker, you should look the frequency response chart of the speaker under evaluation to state this.

2) Inertia is most important at lower frequencies IMHO, higher frequencies don't cause the coil and the cone to move that much because the wave length is way shorter at higher frequencies. Proof of this can be heard when you play through a speaker at low volumes, the highs are there, but to get lows you need to raise the volume.

3) Reactance - That's one important piece of the puzzle...and...I guess you're talking about Inductive Reactance ( since the coil's stray capacitance is so little that it can be surely neglected together with its Xc at audio frequencies ).
Speakers have a nominal impedance, but in the real world impedance changes with frequency, being the square root of the coil resistance squared ( "real" part of the impedance, not frequency dependent ) plus the Inductive Reactance squared ( "imaginary" part of the impedance, frequency dependent ). And, yes, it actually increases with frequency, because Xl = 2Pi*F*L ( Inductive Reactance ).

If the speaker is rated for a -3db response, at 15khz, you would be "hearing", "half" of the nominal 1 khz sound pressure. I once used butyl to dampen harsh highs from a small speaker by coating the entire cone with it. It worked well but was not "Hi-Fi"

The frequency response means that is what can be heard, assuming the listener's hearing is good, and they are in the normal sound field, ie on-axis and at a reasonable distance to the speaker.
A regular guitar amp might have trouble putting out full power at 15kHz, especially if the speaker impedance may be >2x the nominal , but most guitar speakers are way down by then. As am I. Peter.